This invention relates to an improved fluid operated, double diaphragm pump, and, more particularly, to the pilot valve construction for such a pump.
Heretofore the use of a double diaphragm pump to transfer highly viscous liquids has been known. Typically such a pump comprises a pair of pumping chambers with a pressure chamber arranged in parallel with each pumping chamber in a housing. Each pressure chamber is separated from its associated pumping chamber by a flexible diaphragm. As one pressure chamber is pressurized, it forces the diaphragm to compress fluid in the associate pumping chamber. The fluid is thus forced from the pumping chamber. Simultaneously, the diaphragm associated with the second pumping chamber is flexed so as to draw fluid material into the second pumping chamber. The diaphragms are reciprocated in unison in order to alternately fill and evacuate the pumping chambers. In practice, the chambers are all aligned so that the diaphragms can reciprocate axially in unison. In this manner the diaphragms may also be mechanically interconnected to ensure uniform operation and performance by the double acting diaphragm pump.
Various controls have been proposed for providing pressurized fluid to the chambers associated with the double acting diaphragm pump. It is important to provide some type of pilot valve arrangement which will shift the flow of pressurized fluid to the appropriate pressure chamber. Most previous diaphragm pump pilot valve designs produce a momentary signal at the end of each pumping stroke to effect the shift of fluid flow. That momentary signal is typically removed by reversal of movement of the diaphragms.
When pumps are operated at a very slow cycle speed or pumping very heavy or viscous material, the over travel of the diaphragm is reduced. The duration of the pilot or shift signal is also shortened. This may cause only partial shifting of the pilot valve or stopping of the pilot valve in a center position thereby incapacitating the pump. The present invention is designed to overcome this deficiency associated with prior art designs.